1. Field of the Invention
The present invention relates to an electronic apparatus, such as a solid state imaging device or an imaging apparatus, an AD converter, and an AD conversion method.
2. Description of the Related Art
In an electronic apparatus, an analog signal is often converted into digital data (called AD conversion). A difference between two analog signals (voltage levels) maybe converted into digital data. As an AD conversion method, various methods may be considered in terms of circuit size, processing speed (improvement in the speed), resolution, and the like. As an example, there is a reference signal comparing type AD conversion method (see JP-A-2005-323331). In addition, the reference signal comparing type is also called a slope integration type or a ramp signal comparing type.
In the reference signal comparing type AD conversion method, a reference signal whose value changes gradually is used for voltage comparison for conversion into digital data. In addition, an analog signal to be processed is compared with the reference signal, and the digital data of the signal to be processed is acquired on the basis of the count value obtained by performing count processing in a count operation effective period based on the comparison processing result.
JP-A-2005-323331 discloses an example in which the reference signal comparing type AD conversion method is applied to a solid state imaging device or an imaging apparatus. In performing CDS processing by calculating the difference between a signal level and a reset level at the pixel signal voltage, the CDS processing is simultaneously performed at the time of reference signal comparing type AD conversion. By acquiring the digital data as a result of the difference between the reset level and the signal level, digital data of a signal component from which noise has been removed is acquired.
In the method disclosed in JP-A-2005-323331, the total AD conversion period is shortened by setting the count period of the reset level to be shorter than that of the signal level while maintaining the inclination (rate of change) of a reference signal constant for both the reset level and the signal level.